/**
给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。 

 

 示例 1： 
 
 
输入：head = [1,2,3,4,5], n = 2
输出：[1,2,3,5]
 

 示例 2： 

 
输入：head = [1], n = 1
输出：[]
 

 示例 3： 

 
输入：head = [1,2], n = 1
输出：[1]
 

 

 提示： 

 
 链表中结点的数目为 sz 
 1 <= sz <= 30 
 0 <= Node.val <= 100 
 1 <= n <= sz 
 

 

 进阶：你能尝试使用一趟扫描实现吗？ 

 Related Topics 链表 双指针 👍 2478 👎 0

*/

package com.shuzijun.leetcode.editor.cn;
public class RemoveNthNodeFromEndOfList{
    public static void main(String[] args) {
         Solution solution = new RemoveNthNodeFromEndOfList().new Solution();
    }
    //leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        //fast先到第n个节点处
        ListNode fast = head;
        int count = 0;
        while (fast != null){
            count++;
            if (count == n){
                break;
            }
            fast = fast.next;
        }

        if (fast == null){
            return head;
        }

        ListNode slow = head;
        ListNode pre = null;
        while (fast.next != null){
            fast = fast.next;
            pre = slow;
            slow = slow.next;
        }

        if (pre == null){
            head = head.next;
        }else {
            pre.next = slow.next;
        }

        return head;
    }
}
//leetcode submit region end(Prohibit modification and deletion)

}